I am having the same problem. It said carrier update available and now I have no service.
I followed the Apple instructions to update with my computer. Still no service.
What is the next step?
Hello, bbars. Apple reported that a small percentage of iPhone 7 devices experienced a component fail on the main logic board, causing the device to show “No Service” even if cellular coverage was available. For more information, refer to https://www.apple.com/support/iphone-7-no-service/